This invention is generally directed to a photoresponsive imaging device, and more specifically to layered photoresponsive devices, and the use of such devices in electrophotographic imaging systems.
Electrophotographic copying, and more specifically xerography as described in U.S. Pat. No. 2,297,691, involves the development of an electrostatic latent image on the surface of a photosensitive plate or photoreceptor, which is comprised of a conductive substrate containing on its surface a layer of photoconductive insulating material. In some instances there is included a thin barrier layer between the substrate and the photoconductive layer, such as aluminum oxide, to prevent charge injection from the substrate to the photoconductive layer upon charging of the plate surface.
In one known method a latent image is formed on the photoreceptor surface by first charging the plate in the dark, such as by exposing it to a cloud of corona ions, and imaging by exposing the plate to a light and shadow image, for the purpose of selectively discharging the photoreceptor, whereby a latent image corresponding to the shadow areas is formed. This latent electrostatic image is then developed by contacting the plate surface with a developing material such as toner, which will adhere to the latent image due to electrostatic attraction. The toned image can then be transferred to a substrate such as paper, followed by subsequent fusing of the toner into the paper thereby forming a permanent copy.
The imaging surface of the photoreceptor is then cleaned by any of several known methods, including charging, the purpose of the cleaning generally being to remove any residual toner and/or the electrostatic latent image. Also the electrostatic latent image can be used in a number of other ways such as for example, electrostatic scanning systems may be employed to read the latent image or the latent image can be transferred to other materials by TESI techniques and stored. The developed image can also be read or permanently affixed to the photoconductor when the imaging layer is not to be reused.
Numerous types of photoreceptors can be used in the above-described method, and are well-known, such photoreceptors including for example, organic materials like polyvinylcarbazole, inorganic materials such as selenium and selenium alloys, and mixtures thereof. Photoreceptors are also known wherein the charge carrier generation and charge carrier transport functions are accomplished by discrete contiguous layers. Also known are photoreceptors which include an overcoating layer of an electrically insulating polymeric material, and in conjunction with this overcoated type photoreceptor there have been proposed a number of imaging methods, such as the method described, for example, in the text by R. M. Schaffert on Electrophotography published by Focal Press Limited, London, 1975. In one process there is used a non-ambipolar photoconductor wherein charge carriers are injected from the substrate electrode into the photoconductor surface. In such a system in order to obtain high quality images the injecting electrode must satisfy the requirements that it injects charge carriers efficiently and uniformly into the photoconductor.
While imaging systems and devices have been described in copending applications, similar to the device of the present invention such devices are primarily directed to layered structures comprised mostly of organic substances, for example the transport layer can be organic, and different types of injecting electrodes are used. While these devices function adequately, there continues to be a need for improved photoreceptor devices, and more specifically layered inorganic photoreceptor devices which have excellent injecting properties, and therefore can be used in electrophotographic systems for the purpose of obtaining images of high quality over a long period of time.